The National Academy of Sciences In everyday usage: "theory" often refers to a hunch or a speculation. The word, “theory” is often used when drawing a conclusion based on inconclusive evidence. The formal scientific definition of theory: It refers to a comprehensive explanation of some aspect of nature that is supported by a vast body of evidence.

National Academy of Sciences “Scientific theories are so well-established that no new evidence is likely to alter them substantially.” Example: No New Evidence will Demonstrate:Example: No New Evidence will Demonstrate: –that the Earth does not orbit around the sun (heliocentric theory) –that living things are not made of cells (cell theory) –that matter is not composed of atoms (atomic theory) –that the surface of the Earth is not divided into solid plates that have moved over geological timescales (the theory of plate tectonics) How does this relate to the theory of evolution?How does this relate to the theory of evolution? –It is supported by so many observations and confirming experiments that the basic components of the theory will not be overturned by new evidence. –However, like all scientific theories, the theory of evolution is subject to continuing refinement as new areas of science emerge or as new technologies enable observations and experiments that were not possible previously.

In the past, people believed in spontaneous generation-- the idea that nonliving material can produce life out of no-where. (if you had corn, mice would appear) After all, maggots magically appeared on meat as if out of nowhere.

This idea was disproved by the microscope. Micro-organisms are all over the place. But if living things only come from other living things, then where did the first living thing come from? Francesco Redi

This is a question that scientists have hypothesized and theorized over: What is the scientific explanation of how life first appeared on our planet?????

Scientists hypothesize that on primitive Earth it was very hot, where lava and toxic gases were constantly spewed from volcanic eruptions- not conditions conducive to life as we know it.

We have no record of life’s origin, probably because movements in the mantle and crust, volcanic activity, and erosion obliterated all traces of it. The oldest fossils of living things that have been found resemble anaerobic prokaryotes (single-celled bacterium that did not require oxygen) We can however put together possible scientific explanations of how life originated by considering three questions: -Can we identify physical and chemical conditions that prevailed on the Earth when life originated?......HOW COULD WE DO THIS? -Do the known principles of physics, chemistry, and evolution support or disprove the hypothesis that large organic molecules (Bio-molecules) formed spontaneously and evolved into the fundemental properties of life? -Can we design experiments to test the hypothesis that living systems emerged through chemical evolution?

By studying primitive rock and young planets much like ours, scientists theorize that….. Earth’s early atmosphere consisted of: - water vapor (steam) - hydrogen - ammonia ( NH³) - methane (CH ) 4 There was no free oxygen ( O 2 ) on our planet.

Living organisms are made of four main bio-molecules. Many scientists have hypothesized and theorized how the gases on primitive Earth could have joined together to form bio-molecules so that life could occur. Carbohydrates Lipids Proteins Nucleic Acids

Russian scientist (1930s), Alexander Oparin hypothesized that life began in the oceans. He believed that energy from the sun, heat, and lightning from constant storms triggered chemical reactions that caused different molecules on Earth to join together to form bio-molecules.

In 1953, two American scientists Miller and Urey actually tested Oparin’s hypothesis by simulating conditions of early Earth. After their experiment, they discovered that amino acids, sugars, lipids, and other organic molecules had formed in the “oceanic compartment!” These molecules were formed from ABIOTIC factors. They added the atmospheric gases that were said to be present at the time. They added water vapor. They added electricity to simulate the lightning present.

From there, various other experiments were created and carried out to take the data further- can these subunits bond together to form acutal bio-molecules?…..after amino acids were heated without oxygen, they began to link and form proteins. (NA as well) In 1992 a biochemist named Sidney Fox produced very simple cell-like structures called protocells by heating the proteins and other bio-molecules together. Amino acids join to form proteins

Before there were oceans When oceans were forming Early oceans and atmosphere Our oceans today

Science tells us the Earth is very old. 4.6 billion years give or take! Geologists have organized Earth’s history into different periods. The largest intervals of geologic time are called EONS and are hundreds of MILLIONS of years long. EONS

Eons are broken down into ERAS Phanerozoic Eon (the present eon) is divided into three eras: Paleozoic, Mesozoic, and the present Cenozoic. ERAS

Eras are lastly broken down into PERIODS We are currently in the Quarternary period of the Cenozoic Era. PERIODS TERTIARY

Lets start at the beginning and make our way to NOW.

The Precambrian Eon ● Makes up 87% of Earth’s history thus far ● It includes the hypothesized beginning of Earth 4,600,000,000 Billion years ago up to 544,000,000 Million years ago (so it was approx. four billion years long) It includes when prokaryotes formed….then eukaryotes….plants, then to simple invertebrates near the end of this eon (according to fossil records)

The Phanerozoic Eon ● Goes from 544,000,000 Million years ago to the present. ● This Eon includes: multi-cellular animal species explosions several mass extinctions dinosaurs humans Ice Ages